This invention relates to a fixture of universal type for locking motorcycle wheels in general onto the shaft of balancing machines.
The hub of such wheels is known to be provided with rolling bearings enabling the wheel to be centered on the balancing shaft, but not rotated by it.
Consequently, the shafts of machines for balancing motorcycle wheels must be provided with means for rotating the wheel.
An example of such means is described in U.S. Pat. No. 4,489,608, the text of which is to be understood as totally included in this description for opportune reference.
These comprise a wheel carrier spindle which is coaxially fixed to the end of the balancing machine shaft, and on which there are slidingly mounted, starting from a shoulder rigid with said shaft, at least one spring, a first centering cone to engage one end of the hub of a motorcycle wheel mounted on the spindle, a second centering cone to engage the opposite end of said hub and provided with means for forcing it towards said first cone, and at least one elastically deformable dragging member rigid with the shaft and surrounding said at least one spring and said first centering cone, to contact a wheel portion external to the hub.
In the aforesaid known system, before mounting the wheel to be balanced said at least one spring is in the completely unloaded state, and said at least one dragging member, such as a rubber ring or the like, is distant from the wheel.
When the wheel has been mounted on the wheel carrier spindle, practically in contact with the first centering cone, or inner cone, it is pushed towards the machine structure causing the second centering cone, or outer cone, to move axially along said wheel carrier spindle.
Said axial movement causes the inner cone to withdraw against the resistance offered by the at least one spring which, by loading, provides the force for locking the wheel hub between the two cones.
The said axial movement also brings said at least one elastically deformable dragging member into contact with the wheel portion external to the hub, with the result that the wheel is torsionally engaged with said shaft.
The aforedescribed known system has proved unsatisfactory at least for the following reasons.
Firstly, it does not allow independent adjustment of the force used to axially lock the wheel and the force used to engage the dragging member with the wheel. Moreover, said system can result in measurement errors, hence balancing errors, because of misalignments which can exist between said at least one dragging member and the wheel carrier spindle, in particular if said at least one dragging member is not rigid with the shoulder on the balancing machine shaft, and above all if the said dragging member comprises two or more adjacent rings separated from each other.
The main object of the present invention is to obviate the aforestated drawback within the context of a simple, rational and reliable construction.
Said object is attained by a fixture presenting the characteristics indicated in the claims.
It comprises a spindle to be removably fixed onto the direct extension of the balancing shaft to receive the hub of the wheel to be balanced, means for fixing the hub onto the spindle, and means for rotating said wheel about the axis of said shaft.
According to the invention, said means comprise two independent operating devices, to be described in detail hereinafter, of which one, known as the locking device, is provided to axially secure said hub onto said spindle, and the other, known as the dragging device, comprises a dragging part arranged to slide parallel to the balancing shaft between a rest position in which it is spaced from the wheel locked on the spindle, and a working position in which it is in contact with a wheel portion external to the hub. By virtue of the aforestated, all the objects of the invention are attained.
In this respect, the provision of said two independent devices enables the two forces for axially locking the wheel and, respectively, for rotating the wheel about itself, to be chosen as required.